one of the
commonest biochemical sedimentary rocks. It is a grey, white or
yellowish rock mainly composed of calcite. It is easy to idenify with
HCl, and it often contains fossils. Depending on its texture and
can be oolitic,
pisolitic, nummulitic, bryozoan, shelly,
crinoidal, coral or freshwater limestone.
Chalk rock by berduchwal via Flickr.com
Chalk is a
has been formed from
calcite. It may also contain only
small amounts of silt, mud and other minerals such as quartz.
got micro-fossils as well as macro-fossils which include molluscs such
as ammonites, bivalves and echinoids. It is very soft and powdery.
Coal is a
black organic rock which has been formed from dead plant material. It
consists of carbon, and may have plant fossils. Depending on the
formation stage, coal can be either powdery and sooty or shiny and
compact. A stage between plants and coal is peat - an intermadiate
stage where plant material is still visible.